1. Field of the Invention
The present invention relates to a data memorizing device capable of recording or reproducing data by a relative movement between a disk-like recording medium carrier which records data by causing a change in a physical condition on the surface of the recording medium carrrier and a magnetic head placed near the surface of the recording medium carrier.
2. Discussion of Background
FIG. 4 is a cross-sectional view showing a conventional data memorizing device similar to that disclosed in, for instance, Japanese Unexamined Patent Publication 101777/1985, and FIG. 5 is a block diagram showing a position-determining control system for the data memorizing device.
In FIG. 4, a reference numeral 1 designates a base, a numeral 2 designates a spindle motor fixed to the base, a numeral 3 designates a disk-like recording medium carrier, namely, a magnetic disk attached to the rotary shaft of the spindle motor, a numeral 4 designates a magnetic head held near a surface of the magnetic disk 3. The magnetic head 4 is adapted to convert an electric signal into a change of magnetic condition on the surface of the magnetic disk 3 or to convert a change of the magnetic condition into an electric signal. A numeral 5 designates a spring for urging the magnetic head 4 to the magnetic disk 3 by its spring action, numeral 6 designates an arm for fixedly supporting the compression spring 5, numeral 10 designates an actuator adapted to move the magnetic head 4 in the radial direction of the magnetic disk by the aid of the arm 6 and the spring 5 and numeral 11 designates a carriage for supporting the arm 6, the carriage being movable on the base 1 by means of bearings.
A driving coil 12 is mounted on the carriage 11. A position sensor 13 comprises an optical scale fixed to the carriage 11 and a transducer fixed to the base 1. A numeral 15 designates a yoke for forming a magnetic path and a numeral 16 designates a magnet attached to the yoke.
In FIG. 5, reference numeral 20 designates a computer for processing data for controlling the position and the speed of the magnetic head 4, numeral 21 designates a servo circuit which receives a position-determining instruction signal from the computer 20 and drives the carriage 11 by actuating the driving coil 12 in the actuator 10. Also, the servo circuit 21 is adapted so that it receives a position signal indicating the position of the magnetic head 4 detected by the position sensor 13 on the magnetic disk 3 and a speed signal obtained by differentiating and shaping the position signal. It compares, on one hand, the position-determining instruction signal from the computer 20 with the position signal, and on the other hand, a speed-determination signal from the computer 20 with the speed signal from a speed demodulation circuit 22, which differentiates and shapes the position signal detected by position sensor 13 and outputs a signal indicative of position-determining time which corresponds to a time required from the starting position-determining operation to the finish of it. A numeral 23 designates a read/write circuit which receives a data recording/reproducing instruction signal from the computer 20 to record the data in the magnetic disk 3 or to reproduce the data stored in the magnetic disk 3 through the magnetic head 4.
A reference numeral 24 designates an error detection circuit which receives a reference time signal from the computer 20 and the position-determining time signal from the servo circuit 21, and outputs a position-error signal in accordance with the determination that there takes place an error in positioning the magnetic head when the value of the position-determining signal is greater than the value of the reference time signal. The reference time signal corresponds to a reference position-determining time which is determined by the computer 20 on the basis of a distance of moved by the magnetic head 4 on the magnetic disk 3 and a speed pattern obtained by the movement of the head 4.
The operation of the conventional data memorizing device having the construction as above-mentioned will be described.
When the magnetic disk 3 is rotated at a predetermined revolution by driving the spindle motor 2, it produces a viscous air stream on and near the surface of the magnetic disk 3 and a floating force is applied to the magnetic head 4 which is held in the vicinity of the recording surface, whereby there is obtained a fluid dynamic spacing function by which a predetermined air gap is kept between the magnetic head 4 and the magnetic disk 3 due to the balance between a pressing force by the compression spring 5 and the viscous air stream. Under such condition, when a position-determining instruction signal is supplied to the servo circuit 21 from the computer 20, an electric current corresponding to the position-determining instruction signal is supplied to the driving coil 12 in the actuator 10, whereby a magnetic circuit is formed in the yoke 15, the magnet 16 and the air gap. In accordance with the Flemming's left hand rule, the carriage 11 is driven by the influence of the magnetic field by the magnetic circuit, and the magnetic head 4 is moved in the radial direction of the magnetic disk 3. The traverse movement of the magnetic head 4 is detected by the position sensor 13, which generates a position signal corresponding to the position of the head 4. Further, the position signal is subjected to differentiating and shaping by the speed demodulation circuit 22 to detect a speed signal. The position signal and the speed signal are detected by the servo circuit 21 in which the signals are respectively compared with the position-determining instruction signal and the speed-determination instruction signal from the computer 20, whereby the magnetic head 4 is brought to a predetermined position on the magnetic disk 3. During the above-mentioned position-determining operation, the servo circuit 21 outputs a position-determining time signal which corresponds to the time required for positioning of the magnetic head 4. The error detection circuit 24 receives the position-determining time signal from the servo circuit 21 and compares it with the reference time signal corresponding to the reference position-determining time which has been previously received from the computer 20. In comparison of the signals, when the value of the position-determining time signal is greater than the value of the reference time signal, the servo circuit determines that there is an error in determining the position of the magnetic head 4, whereby the positioning-error signal is outputted. The positioning-error signal is received in the computer 20 in which the signal is subjected to a predetermined data-processing and a position-determining instruction signal is again outputted to the servo circuit 21. 0n completion of the position-determining operation, the read/write circuit 23 commands the magnetic head 4 to record data in the magnetic disk 3 or to reproduce data stored in the magnetic disk 3 by receiving a recording or reproduction instruction signal from the computer 20.
However, the conventional data memorizing device has a disadvantage as follows. When a foreign substance enters in the gap formed between the magnetic head 4 and the surface of the magnetic disk by the fluid dynamic spacing function, or strong vibrations or a strong shock is applied to the base 1, the magnetic head 4 may come to contact with the surface of the magnetic disk 3 to thereby damage either the surface of the magnetic disk 3 or the head 4. The damaged surface of the magnetic disk or the magnetic head 4 causes a change in a floating force applied to the head 4. If such an undesirable state remains for a long time, the magnetic head 4 drops on the magnetic disk 3 to thereby cause data stored in the magnetic disk 3 to be lost.